1. Field of the Invention
The invention relates to the spiral binding of perforated sheet groups, and more particularly to the use of plastic thread for the spiral binder.
2. Description of the Prior Art
Plastic spiral binders for sheet groups have certain advantages over metal spiral binders in terms of resistance to damage, particularly in cases where the ends of two binders are accidentally hooked together. In the past, plastic spiral binders have been performed and later inserted in the sheet groups.
A search on the subject matter of this invention revealed the following prior art: The patent to Tauber, U.S. Pat. No. 2,808,079 of Oct. 1, 1957, relates to a book binding machine in which there is a spool of material referred to as wire or some other similar material which is formed into a spiral threaded into the notebook and severed all in one machine. Although this patent does imply that other material might be used, it does not have any heating or cooling arrangement in the structure, and therefore it does not appear that plastic could be formed.
The patent to Penner, U.S. Pat. No. 2,638,609 of May 19, 1953, illustrates a machine for binding books in which plastic coils are used for the binding; however, this machine does not form the coils.
The patent to Griffin, U.S. Pat. No. 3,940,228 of Feb. 24, 1976, was selected as being of general interest as it shows the forming of a coil in plastic material, however, this is on a telephone cord rather than book binding spiral.